Presence of Cp. psittaci in fresh faecal droppings of vaccinated and placebo-vaccinated bird pairs following challenge. Two groups were compared using the Mann–Whitney U test. On all time points, except the day of the challenge, placebo-vaccinated bird pairs showed significantly (p < 0.001) higher median culture scores as compared to the vaccinated group. Bars indicate 25 and 75 percentiles around each median.